DNAF-1: An Analytical Fallout Prediction Model and Code

DNAF-1 has been developed to rapidly predict fallout gamma ray activity from surface burst nuclear explosions. It is suitable for use in large- scale damage assessment studies. Explosion energy yield range is .001 to 100,000 KT. Minimum input data requirements of the code are total and fission yields, speed and direction angle of a single effective wind vector, and a wind shear parameter. Wind data in terms of a vertical profile of wind vectors may be supplied by the user, in which case the code will process the data such as to compute the effective wind vector and shear parameter. The code will automatically compute and print a fallout map in terms of h plus 1 hour exposure rate ordinates for a spatially undistorted array of points on the ground. Alternatively, the user may specify his own map boundaries and grid increments. He also may specify any number of ground points at which the code will compute H pule 1 hour exposure rate and maximum effective biological dose. Both model and code are fully documented, and user instructions for the code are presented. Results of a validation study are presented. Predicted fallout patterns are compared with observed patterns for five test shots that cover a wide range of energy yields. Predictions by the DELFIC and WSEG-10 models also are included. Visual comparisons of contour maps and various statistical comparison methods are used. DNAF-1 predictions are found to be substantially better than those of WSEG-10 and almost as good as DELFIC predictions.